Leaving a game, but still getting points to missions

I am not entirely sure if this would classify as a bug or not, but I will place it here either way.

While in the middle of a game, my internet went down, and I was forced to just wait. When the internet came back up, the match was already over and I was presented with the screen after the game ends.

I showed up as leaver, however I still got points towards a mission that I was currently working on.

Again, not sure if this is a bug, or if it's meant to happen. I am guessing that it is not a bug since Riot wouldn't reward people that leave games.